1. Technical Field
This invention relates to a stage positioning apparatus, and relates in particular to a stage positioning apparatus suitable for placing a specimen in semiconductor device manufacturing and inspection apparatus.
2. Background Art
Various processing and observations in semiconductor manufacturing and inspection apparatuses are usually carried out by placing the specimen on an x-y stage.
In recent years, integrated circuit density has increased significantly, and consequently, line width and interline spacing of circuits has become smaller and micro-sized. Particularly, for sub-micron lithography, in order to secure high precision positioning in the layering of circuit patterns, it is essential to precisely position the patterns. High speed handling of the patterns is important for productivity.
However, conventional x-y stages are operated by feedback control of some actuators, for example, servo motors, provided on the x-y stage to move the stage by means of a ball screw and other arrangements. With such devices involving mechanical friction, positioning has not always been performed satisfactorily at high speed and high precision. Further, even for devices based on air bearings and linear motors to avoid mechanical friction effects, there is a problem that the positioning apparatus can be affected by acceleration and deceleration effects of a moving stage. The stage can be affected by excitation of fundamental frequencies, which adversely affects the accuracy of positioning.
For example, for a scan type stepper device, it is necessary to move the x-y stage smoothly at high speed and high precision. Thus, there has been an increasing demand for a high precision and high productivity x-y stage for positioning specimens for measuring or fabricating purposes in a semiconductor manufacturing apparatus. Similar needs exist for electron microscopy, such that positioning must be carried out at sub-micron accuracy precisely and quickly. Such precision positioning devices are sensitive to vibration, such that even though precision positioning has been originally performed, that position can be lost later due to vibration.
For this reason, vibration elimination devices are used to isolate or attenuate the vibrations that can be transmitted from an installation floor or external disturbances transmitted through air, such as air conditioning. However, vibrations that can be controlled by such vibration elimination devices are limited to those produced by the x-y table. For example, even if a semiconductor fabrication apparatus is placed on an anti-vibration table, it is not possible to control the vibration of an optical beam used to fabricate a specimen inside an apparatus for semiconductor manufacturing. For this reason, when positioning is required at sub-micron level precision in a specimen, the optical beam itself may be displaced by vibration such that the most important aspect in the fabrication, i.e., the beam position, cannot be precisely aligned.
This invention was made in light of the background described above, and it is an object of the present invention to provide a micro-positioning apparatus to enable stable and rapid positioning of a stage on which a specimen is placed. Also, another object is to provide a stage positioning apparatus that has a compact design and a low amount of leakage of magnetic flux and can be operated in a vacuum environment.
An apparatus for positioning a stage comprises a stage for placing a specimen to be radiated with a beam, actuators for levitating the stage and controlling a movement of the stage, a first position sensor for measuring a relative displacement between the stage and the actuators, a second position sensor for measuring a relative displacement between an actual radiation position of the beam on the specimen and a target radiation position, and a controller for positioning the stage so as to decrease the relative displacement detected by the second sensor.
According to this invention, the stage is directly positioned by measuring the relative displacement between the actual radiation position of the beam used for fabrication or measuring of the specimen and the target radiation position, and the stage is moved so as to decrease the relative displacement. By this process, the beam is accurately positioned on the target radiation position. This process enables micro-positioning of the beam to be carried out even when the beam itself or the stage itself is vibrating, for example, in a semiconductor production facility.
A magnetically levitated stage comprises a levitation body having a table section for placing a specimen and side plates extending from outer peripheries of the table section, and actuators for levitating and positioning the levitation body by controlling magnetic force generated by electromagnets therein, the actuators being surrounded by the table section and the side plates, wherein the actuators have permanent magnets disposed near a center section thereof for supporting the weight of the levitation body, electromagnets for controlling horizontal positioning which are disposed in four corners in an outer periphery thereof, and electromagnets for controlling vertical positioning which are disposed in a middle section between the electromagnets for horizontal positioning.
In accordance with the present invention, a compact stage positioning apparatus has been provided by disposing electromagnets and permanent magnets serving as actuators inside a boxed space having bottom opening of a levitation body.